Fig. 1. Sections of ovaries from wild-type and mutant mice at P4-5 stained with haematoxylin and eosin. Ovaries from 50% of TrkB^–/– mice from a mixed genetic background and all mice from the congenic C57BL/6 background have grossly abnormal ovaries that contain greatly reduced numbers of follicles. (A) TrkB^+/+,TrkC^+/+ ovary, containing many follicles. (B) TrkB^–/– ovary on C57BL/6 x 129Sv background with only few follicles remaining (arrowheads). (C) Unaffected TrkB^–/– ovary on C57BL/6 x 129Sv background, which contains as many follicles as (A). (D) Ovary from fourth generation C57BL/6 congenic TrkB^–/– mouse, which contains large areas of cell death and only a few follicles (arrowhead). Scale bars: 20 µm.